Ethylene glycol (EG) is an important organic chemical raw material, which is mainly used for producing polyester fibers, antifreezes, unsaturated polyester resins, lubricants, plasticizers, non-ionic surfactants and explosives etc. In addition, ethylene glycol can also be used in such fields as coating, photographic developer, brake fluid and ink, as the solvent and medium of ammonium perborate and for producing special solvents like glycol ether. Ethylene glycol has a wide range of uses, including a very important use as the basic raw material for producing the polyester(PET) of polyester fibers, Ethylene glycol here being generally referred to as the fiber-grade ethylene glycol product.
At present, both domestic and foreign large-scale ethylene glycol productions mainly adopt the oil route, i.e., direct hydration or pressure hydration process route. According to said process, ethylene oxide and water are compounded to a mixed aqueous solution by 1:20˜22 (molar ratio); said mixed aqueous solution reacts in a fixed bed reactor for 18˜30 minutes at 130˜180° C. and 1.0˜2.5 MPa; ethylene oxide is completely converted into mixed alcohol; and the resultant ethylene glycol aqueous solution has a content of about 10% (by mass); ethylene glycol is then obtained by dehydration concentration and vacuum rectification separation using a multi-effect evaporator. However, the production device requires the installation of multiple evaporators and consumes a large quantity of energy used for dehydration, which results in long running of the production process, more equipments and high energy consumption.
Currently, from a global point of view, the oil resource is increasingly in short supply. Moreover, the world sees great oil price fluctuations. The pattern of the resources in China can be summarized as having less oil, less gas, and more coal. The development of C1 chemical industry, which can not only make full use of the natural gas and coal resources and reduce the dependence on oil imports, but also can reduce the pressure on the environment, is a very important area for research. It is a quite attractive coal chemical industry route to prepare oxalate using carbon monoxide as the raw material and then prepare ethylene glycol by hydrogenating oxalate. Nowadays, both domestic and foreign researches into preparing ethylene glycol by using carbon monoxide as the raw material have achieved excellent effects. The industrial production thereof has been mature. However, as regards the preparation of ethylene glycol by the hydrogenation of oxalate, there is still more work needing further research, especially the hydrogenation of oxalate, wherein more byproducts are produced, and the existence of trace amounts of unsaturated double bond-containing compounds will affect the quality of the ethylene glycol products. One important index for measuring the quality of the fiber-grade ethylene glycol products is the UV-light transmittance at 220 nm, because it will affect the luster and chrominance of the downstream polyester products. As regards the ethylene glycol produced by the oil route, it is generally considered that the important factors affecting the UV-light transmittance at 220 nm of the fiber-grade ethylene glycol products are the aldehyde-containing byproducts present in the products. As for the ethylene glycol products produced by the hydrogenation of oxalate, it is generally believed that the important factor affecting the UV-light transmittance at 220 nm of the ethylene glycol products is different from that of the oil route; generally, less aldehyde-containing byproducts are produced; other non-aldehyde carbonyl compounds may be the important factors affecting the UV-light transmittance at 220 nm of the ethylene glycol products.
The prior art usually uses ion exchange resin as the catalyst to refine and purify ethylene glycol, e.g., U.S. Pat. No. 6,242,655 describes a method of using a strongly acidic cation exchange resin as the catalyst, wherein after the treatment, the content of the aldehyde group in the ethylene glycol products decreases from 20 ppm to 5 ppm or less. However, the defect of the existing method is that the content of the aldehyde group in the ethylene glycol products can only be removed to about 2 ppm at most, but the UV-light transmittance at 220 nm of the ethylene glycol products at this moment still does not reach a very ideal value. Meanwhile, the existing method only applies to ethylene glycol products of the oil routes. The effect of said method on the coal-based products has not been reported. Therefore, how to improve the UV-light transmittance of the coal-based ethylene glycol products and further guarantee the quality of the products is a very important research subject. At present, literature or report on said subject is seldom disclosed.